A thermal printer creates colored prints by transferring dye contained in a donor web to a receiver as the receiver travels a path about a drum. The donor web is placed between the thermal print head and the receiver which is fixed to the drum. The thermal print head is loaded against the drum during the print cycle by a spring. Constant pressure is required to be maintained to insure the integrity and uniformity of the dye transfer process. As the donor advances during the print cycle, it normally contacts the front of the head and contributes a vertical force component which can compromise the constant head load. Accordingly, it will be appreciated that it would be highly desirable to have a donor web movement system which does not compromise the constant head load.
U.S. Pat. No. 4,834,563 which issued May 30, 1989 to Naohiro Ozawa, Toshihiko Gotoh and Junichi Shoji; U.S. Pat. No. 4,739,341 which issued Apr. 19, 1988 to Jyunichi Matsuano and Masaski Yoshida; and U.S. Pat. No. 4,507,667 which issued Mar. 26, 1985 to Kiyoshi Tsuboi disclose thermal printing apparatus wherein a roller assembly is attached to the print head and contacts the donor web after the donor emerges from the nip between the print head and the drum. The roller assembly keeps the donor web and receiver media together after emerging from the nip to help ensure uniform color transfer. In addition to helping ensure uniform color transfer, the roller assemblies also change the angle of the donor web as it emerges from the nip. This change of angle changes the path of the donor web somewhat as it exits the nip but has no effect on the donor entering the nip or as the ink transfer is taking place. Thus, these patents do not address the problem of uneven head loading and may contribute to the problem because the rollers that are attached to the head will effect the head load somewhat as the web tension varies. While these roller structures do help improve print quality or printer performance in a general sense, they have no effect on preventing the varying web tension of the donor from effecting the head load. Accordingly it will be appreciated that it would be highly desirable to have a simple structure for varying web tension without effecting the head load.